Recording tapes having a metal layer applied by vapour deposition



Dec. 6, 1955 A. ORTLIEB ET AL RECORDING TAPES HAVING A METAL LAYER APPLIED BY VAPOUR DEPOSITION Filed Jan. 7, 1952 METAL ALLOY 12 TAPE 7N l/E N TORS W 0%; w 2M MEN 1:, A TTORNEyS United States Patent RECORDING TAPES HAVING A METAL LAYER APPLIED BY VAPOUR DEPGSITION Alfred ()rtlieb, Stuttgart-Vaihingen, and Eberhard Traub, Stuttgart, Germany, assignors to Robert Bosch G. m. b. H., Stuttgart, Germany Application January 7, 1952, Serial No. 265,304

2 Claims. (Cl. 117-227) The invention concerns a recording strip or tape having a very thin metal layer applied, for example, by vapour deposition, in which traces are burnt or etched by the passage of an electric current.

in the known method for burning or etching such tracings into the metal layer of the recording tape, the latter is moved relatively to one or more recording electrodes to which an electric potential is applied and through which passes the recording current. Between each recording electrode and the metal layer, there should be as small a contact surface as possible resulting in a consequently large contact resistance, whilst between the metal layer and a contact roller connected to the source of potential there should, however, be as great a contact surface as possible resulting in a correspondingly small resistance.

When carrying out this process, recording tapes were used having metal layers of zinc or cadmium which were applied by thermal evaporation in a vacuum or by sputtering or similar methods, and measured from 0.02 to 0.2; in thickness. Such metal layers, however, cannot be produced in all cases in such a manner that neat traces are formed even with burning voltages which lie below the minimum arcing voltage. A further disadvantage in the use of zinc or cadmium coatings consists in the fact that they are not sufficiently stable. For this reason it has already been proposed to provide a protective coating on metal coated record tapes after the deposition of the metal layer. On using such recording tapes the electrode or stylus cannot come into direct contact with the metal layer. The burning-out voltage applied must at least be great enough to develop sparks that are capable of puncturing the protective coating.

Electric sparks, however, are in many cases undesirable.

Experiments have shown that one can also obtain good traces at low burning-out voltages, if, according to the present invention, one uses recording tapes or strips having thereon a thin layer of a metal whose melting point lies below that of pure cadmium.

For instance, layers consisting of tin or alloys of, for example, zinc and cadmium, have proved to be particularly suitable.

The tape or strip according to the present invention is illustrated diagrammatically in the accompanying sectional drawing. The tape or strip comprises a base material 12 on which there is deposited a thin layer of metal 14, though it will be understood that for the sake of clarity the base material and metal are each shown to an arbitrary enlarged scale. The present invention is primarily concerned with the metal layer and the base material may be any suitable flexible electrically non- 2,726,179 Patented Dec. 6, 1955 conducting substance conventional in the art, such, for example, as paper or a thermo-plastic.

When using recording tapes with such layers, it is not necessary to produce the trace by means of sparks, because on the one hand, the electrode can slide on the bare metal layer, and on the other hand, the heat produced by the current at the point of contact with the electrode is already sufficient to etch the low melting point metal layer at this point without sparking. Therefore, one can operate with burning-out voltages which lie below the minimum arcing voltage which is approximately 14 volts. Good traces can be burnt in the tape even with a very low voltage of, for example, 6 volts.

The metal layers of the present invention have a very good electric conductance particularly if they are of zinc or contain zinc. Therefore, in contrast to layers of cadmium, little voltage drop occurs as a result of the passage of current between the burning-out point and the point of contact between the metal layer and the contact roller, which should cover as large a surface as possible, and the development of heat is consequently limited to a small area around the burning-out point, whilst the metal layer in the immediate proximity of that point remains cold. The efiect of this during the burning-out is that any parts of the metal layer that are melted recede from the electrode or stylus towards the adjacent colder areas, and causes an uneven thickening or" the metal layer along the trace. On burningout or etching the trace by means of arcing, however, the major portion of the layer substance which is burnt or etched away evaporates, settles on the stylus partially in the form of an oxide deposit and often necessitates constant cleaning of the electrode or stylus.

If, for example, the metal layer consists of an alloy containing substantially of cadmium and substantially 20% of zinc and having a melting point of approximately 270 C., then perfectly neat traces can be readily burnt or etched therein at a temperature which lies approximately 40 C. lower. This is due to the fact that the metal layer is very thin, generally approximately 0.1 and therefore is readily punctured at a temperature which lies below its melting point.

In addition to these advantages, layers of a cadmiumzinc alloy also have the particular advantage that they possess a high degree of stability and therefore can be stored for a long period without the layers deteriorating.

We claim:

1. As a new article of manufacture, an electrically non-conductive recording tape having a thin vapour deposited layer from .02 to .Z in thickness of an alloy of cadmium and zinc containing substantially 80% of cadmium.

2. As a new article of manufacture, an electrically non-conductive recording medium having a thin vapour deposited layer from .02 to .2,u in thickness of an alloy of cadmium and zinc containing substantially 80% of cadmium and substantially 20% of zinc.

References Cited in the file of this patent UNITED STATES PATENTS 2,274,444 Freed Feb. 24, 1942 2,374,214 Kline et al. Apr. 24, 1945 2,382,432 McManus et a1 Aug. 14, 1945 2,554,017 Dalton May 22, 1951 

1. AS A NEW ARTICLE OF MANUFACTURE, AN ELECTRICALLY NON-CONDUCTIVE RECORDING TAPE HAVING A THIN VAPOUR DEPOSITED LAYER FROM .02 TO .2U IN THICKNESS OF AN ALLOY OF CADMIUM AND ZINC CONTAINING SUBSTANTIALLY 80% OF CADMIUM. 